1. Field of the Invention
The present invention relates generally to lifting window blinds (roll-up blinds, Venetian blinds) and, more specifically, to a center of gravity adjustable bottom rail for window blind. The invention relates to also to a window blind assembly having a center of gravity adjustable bottom rail.
2. Description of the Related Art
FIG. 7 shows a roller blind 90 according to the prior art. This structure of roller blind 90 comprises a barrel 91 fastened pivotally with the top of a window (not shown) in transverse direction, a bottom rail 92 arranged in parallel to and spaced below the barrel 91, flexible slats 93 arranged in parallel between the barrel 91 and the bottom rail 91, two thin covering sheets 95 respectively covering the slats 93 at front and back sides and connected between the barrel 91 and the bottom rail 92 to join the slats 93. The covering sheets 95 soften the light passing through the window blind assembly 90. The user can rotate the barrel 91 (manually or by a motor drive) to roll up the slats 93 and the covering sheets 95 around the periphery of the barrel 91.
The aforesaid roller blind 90 is still not satisfactory in function. Because it is difficult to keep the tension of each covering sheet 95 (which is usually a piece of meshed fabric) in balance at left and right sides, the bottom rail 92 cannot be maintained in horizontal accurately. During fabrication and assembly process of the bottom rail 92 (which is comprised of an aluminum profile and two plastic end caps at two ends of the aluminum profile), it is difficult to have the gravity weight evenly distributed in all directions. When installed in the covering sheets 95, the bottom rail 92 may not be maintained in horizontal accurately. When the bottom rail 92 lifted to a relatively higher position close to the barrel 91, it stands in an oblique position sloping downwards toward one lateral side of the blind (see FIG. 8), obstructing the sense of beauty of the roller blind 90.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a center of gravity adjustment device, which is practical for use in a window blind assembly, such as a roll-up blind, lifting-type blind, etc., for enabling the user to adjust the center of gravity of the bottom rail to keep the bottom rail in horizontal.
It is another object of the present invention to provide a window blind assembly having a center of gravity adjustable bottom rail, which enables the user to adjust the center of gravity of the bottom rail, keeping the bottom rail in horizontal.
To achieve these objects of the present invention, a center of gravity adjustment device is installed in a bottom rail of a window blind assembly for adjusting the center of gravity of the bottom rail, comprising an adjustment wheel fastened rotatably with the bottom rail for rotating by a user, a rotating wheel fastened rotatably with the bottom rail and spaced from the adjustment wheel at a distance, a weight movable in the bottom rail between the adjustment wheel and the rotating wheel, and a cord member mounted around the adjustment wheel and the rotating wheel and fastened to the weight for moving the weight in said bottom rail between the adjustment wheel and the rotating wheel upon rotation of the adjustment wheel.